Do you mean as an adult?
As babies obviously they're tiny
As fully grown adults, I guess about 25g is small, but perfectly healthy. When my boys were getting sick their weight really went down. The Cloud dropped from 37g to 17g at the end and was just a little skeleton. I imagine a really tiny one could be lighter fully grown. Dasher was the runt of his litter so I was expecting him to be tiddly, er not quite eh Dash, 43g today!